The sites in S. typhimurium of mutations causing feedback resistance of anthranilate synthetase and phosphoribosyl transferase will be mapped in the first and second gene of the tryptophan operon. The mutations will be related to structural alterations in the enzymes by "fingerprinting" peptide fragments. The basis for suppression of promoter mutations and stimulation of nonmutant operons by supX mutations will be studied by in vitro protein and mRNA synthesizing systems, by study of the structural nature of the mutant promoters, by the interactins with regulatorymutations and by study of pool sizes of various substrates. The mechanisms for unstable initiation of gene expression will be studied by genetic mapping techniques and factors affecting the formation of tandem chromosomal duplications will be analyzed. Factors affecting recombination within a transducing fragment and the effects of deletions on cotransduction linkages will be studied by genetic mapping techniques.